Feature request: Expose `writeImages`'s `combinePages` option as a new CompareOption

[EvHaus]

The writeImages function in this library has a combinePages argument which is set to true by default. Could you please expose control over this in CompareOptions so that I can set it to false for my usecase?

In my case I'm doing a comparison of a giant 200 page PDF and reviewing the diff of a 150,000px tall PNG is really difficult, whereas reviewing the diff page-by-page would be really lovely.

For now, I'm using this pnpm patch to handle this behaviour. It works great! It would be lovely if the library could support this natively though:

@@ -0,0 +1,24 @@
diff --git a/lib/compare-pdf-to-snapshot.js b/lib/compare-pdf-to-snapshot.js
index c0b8f24a5f35a9f2f2e65a8e06c5bb7047c5ce33..1dce7b4172699930956b22719175259fef9c5519 100644
--- a/lib/compare-pdf-to-snapshot.js
+++ b/lib/compare-pdf-to-snapshot.js
@@ -108,7 +108,7 @@ async function handleMissingSnapshot(pdf, snapshotContext, { failOnMissingSnapsh
     }
     // Generate snapshot if missing
     const images = await (0, pdf2png_1.pdf2png)(pdf, pdf2PngOptions).then(maskImgWithRegions(maskRegions));
-    await (0, imageUtils_1.writeImages)(snapshotContext.path)(images);
+    await (0, imageUtils_1.writeImages)(snapshotContext.path, false)(images);
     return true;
 }
 async function compareWithSnapshot(pdf, snapshotContext, { maskRegions, pdf2PngOptions, tolerance }) {
@@ -119,8 +119,8 @@ async function compareWithSnapshot(pdf, snapshotContext, { maskRegions, pdf2PngO
         await removeIfExists(snapshotContext.newPath);
         return true;
     }
-    await (0, imageUtils_1.writeImages)(snapshotContext.newPath)(images);
-    await (0, imageUtils_1.writeImages)(snapshotContext.diffPath)(result.diffs.map((x) => x.diff));
+    await (0, imageUtils_1.writeImages)(snapshotContext.newPath, false)(images);
+    await (0, imageUtils_1.writeImages)(snapshotContext.diffPath, false)(result.diffs.map((x) => x.diff));
     return false;
 }
 async function removeIfExists(filePath) {

[moshensky]

hi @EvHaus,

I’m a bit tight on time, but can look into it in a week or two. If you’d like to open a PR in the meantime, that’d be very welcome!

[moshensky]

Thanks for the PR!

After reviewing your suggested changes and thinking a bit more about the requirements for per-page snapshots, I drafted a proposal that I’d love your thoughts on.

Please don’t take it as something I expect you to implement — it’s just an idea to align on direction. If it makes sense, I’ll try to find some time to contribute it myself (unless, of course, you’d like to take it on).

Here’s the outline of what I had in mind #99.